This invention relates to an apparatus for the evaluation and diagnosis of tire contributions to erratic motions of a vehicle which are induced when the vehicle travels over longitudinally grooved pavement.
Highways in many parts of the country are frequently grooved to promote drainage of water, affording improved wet traction performance of vehicles. The grooves are sometimes oriented laterally with respect to vehicle motion, but are predominantly oriented longitudinally. This can cause problems because when oriented longitudinally, tires interact with the grooves and produce erratic motions of the vehicle, resulting in perceptions of darty, uncontrollable side displacements (hereinafter referred to as "groove wander"). The actual sideward motions of the vehicle are small in magnitude, not affecting the safe control of the vehicle. However, they contribute to the discomfort of the ride as perceived by the occupants.
It is known that control over the interaction of tire and road grooves resides in the type of highway grooving (viz. width, depth, spacing) and certain mechanical actions and dimensional properties of tires. The most effective means of suppressing the vehicular activity through tire alteration consists of, but is not limited to, varying the distribution of material in the tread by changing the specific patterns of ribs, lugs and voids therein.
Evaluations of the degree of discomfort attributable to tires on a given road surface of the grooved variety have, in the past, been accomplished subjectively by trained individuals experienced with the phenomenon. Substitution of sets of tires on a chosen vehicle readily allows for a comparison of these effects. With sizable accumulation of such performance data, one is eventually equipped to empirically develop tire design criteria, aiding the further development of tires with notably improved responses.
The effects of tread design on this phenomenon of groove wander, due to the interaction of a tire tread and road grooves, has fostered the development of certain analytical techniques for analyzing and diagnosing the spatial relationships of individual tire tread details. These techniques, however, evolved during a time when commercial tires featured circumferential "ribs" (or the appearance of such). The techniques relied on the actual presence, or judicious perception of the presence (by experienced personnel), of these distinguishable "ribs" of tires. The techniques, unfortunately, and for obvious reasons, fall short of application to the more complex tread designs penetrating the tire market in the 1980s. As enhancements in other areas of performance are attained through the implementation of new tread designs and since their acceptance is ever increasing, the industry actively seeks effective methods of analyzing and suppressing "groove wander".
It is, therefore, a primary object of this invention to provide laboratory equipment and procedures for fulfilling industry's needs for: (1) evaluating those mechanical actions of tires which lead to erratic vehicular performance occurring on longitudinally grooved pavements; and (2) diagnosing contributions of different portions of a tire tread to performance achieved on grooved pavement, thereby aiding in the isolation and avoidance of problem conditions.
Further objects and advantages of the invention will become apparent as the following description proceeds.